The Laser Interferometer Gravitational-Wave Observatory "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) Reported on behalf of LIGO colleagues by Fred Raab, LIGO Hanford Observatory

Corps of Discovery detour Snake River Corps of Discovery detour Columbia River LIGO Yakima River The spirit of exploration did not end 200 years ago. A new age of discovery is beginning with LIGO… LIGO

LIGO’s Mission is to Open a New Portal on the Universe In 1609 Galileo viewed the sky through a 20X telescope and gave birth to modern astronomy The boost from “naked-eye” astronomy revolutionized humanity’s view of the cosmos Ever since, astronomers have “looked” into space to uncover the natural history of our universe LIGO’s quest is to create a radically new way to perceive the universe, by directly listening to the vibrations of space itself LIGO consists of large, earth-based, detectors that will act like huge microphones, listening for the most violent events in the universe LIGO

The Laser Interferometer Gravitational-Wave Observatory LIGO (Washington) LIGO (Louisiana) Brought to you by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 400 LIGO Science Collaboration members worldwide. LIGO

LIGO Laboratories Are Operated as National Facilities in the US…

Part of Future International Detector Network Simultaneously detect signal (within msec) GEO Virgo LIGO TAMA detection confidence locate the sources decompose the polarization of gravitational waves AIGO LIGO

Big Question: What is the universe like now and what is its future? New and profound questions exist after nearly 400 years of optical astronomy 1850’s  Olber’s Paradox: “Why is the night sky dark?” 1920’s  Milky Way discovered to be just another galaxy 1930’s  Hubble discovers expansion of the universe mid 20th century  “Big Bang” hypothesis becomes a theory, predicting origin of the elements by nucleosynthesis and existence of relic light (cosmic microwave background) from era of atom formation 1960’s  First detection of relic light from early universe 1990’s  First images of early universe made with relic light 2003  High-resolution images imply universe is 13.7 billion years old and composed of 4% normal matter, 24% dark matter and 72% dark energy; 1st stars formed 200 million years after big bang. We hope to open a new channel to help study this and other mysteries LIGO

Don’t worry, we’ll work around that! A Slight Problem Regardless of what you see on Star Trek, the vacuum of interstellar space does not transmit conventional sound waves effectively. Don’t worry, we’ll work around that! LIGO

John Wheeler’s Picture of General Relativity Theory LIGO

General Relativity: A Picture Worth a Thousand Words LIGO

New Wrinkle on Equivalence bending of light Not only the path of matter, but even the path of light is affected by gravity from massive objects First observed during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster Measurements showed that the light from these stars was bent as it grazed the Sun, by the exact amount of Einstein's predictions. A massive object shifts apparent position of a star The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement of light as gravitational lensing. LIGO

Einstein’s Theory of Gravitation …at work “Einstein Cross” The bending of light rays gravitational lensing Photo credit: NASA and ESA Quasar image appears around the central glow formed by nearby galaxy. The Einstein Cross is only visible in southern hemisphere. In modern astronomy, such gravitational lensing images are used to detect a ‘dark matter’ body as the central object LIGO

Gravitational Waves Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy Rendering of space stirred by two orbiting black holes: LIGO

What Phenomena Do We Expect to Study With LIGO?

Gravitational Collapse and Its Outcomes Present LIGO Opportunities fGW > few Hz accessible from earth fGW < several kHz interesting for compact objects LIGO

The Brilliant Deaths of Stars time evolution Supernovae Images from NASA High Energy Astrophysics Research Archive LIGO

The “Undead” Corpses of Stars: Neutron Stars and Black Holes Neutron stars have a mass equivalent to 1.4 suns packed into a ball 10 miles in diameter, enormous magnetic fields and high spin rates Black holes are even more dense, the extreme edges of the space-time fabric Artist: Walt Feimer, Space Telescope Science Institute LIGO

Catching Waves From Black Holes Sketches courtesy of Kip Thorne LIGO

Gravitational Waves the evidence Emission of gravitational waves Neutron Binary System – Hulse & Taylor PSR 1913 + 16 -- Timing of pulsars 17 / sec · · ~ 8 hr Neutron Binary System separated by 106 miles m1 = 1.4m; m2 = 1.36m; e = 0.617 Prediction from general relativity spiral in by 3 mm/orbit rate of change orbital period LIGO

How does LIGO detect spacetime vibrations? Leonardo da Vinci’s Vitruvian man

Basic Signature of Gravitational Waves LIGO

Power-Recycled Fabry-Perot-Michelson Interferometer suspended mirrors mark inertial frames antisymmetric port carries GW signal symmetric port carries common-mode info, like shifts in laser frequency, intensity LIGO

How Small is 10-18 Meter? One meter, about a yard Human hair, about 100 microns Wavelength of light, about 1 micron Atomic diameter, 10-10 meter Nuclear diameter, 10-15 meter LIGO sensitivity, 10-18 meter LIGO

Some of the Technical Challenges Typical Strains < 10-21 at Earth ~ 1 hair’s width at 4 light years Understand displacement fluctuations of 4-km arms at the millifermi level (1/1000th of a proton diameter) Control arm lengths to 10-13 meters RMS Detect optical phase changes of ~ 10-10 radians Hold mirror alignments to 10-8 radians Engineer structures to mitigate recoil from atomic vibrations in suspended mirrors LIGO

What Limits Sensitivity of Interferometers? Seismic noise & vibration limit at low frequencies Atomic vibrations (Thermal Noise) inside components limit at mid frequencies Quantum nature of light (Shot Noise) limits at high frequencies Myriad details of the lasers, electronics, etc., can make problems above these levels LIGO

Vibration Isolation Systems Reduce in-band seismic motion by 4 - 6 orders of magnitude Little or no attenuation below 10Hz Large range actuation for initial alignment and drift compensation Quiet actuation to correct for Earth tides and microseism at 0.15 Hz during observation BSC Chamber HAM Chamber LIGO

Seismic Isolation – Springs and Masses damped spring cross section LIGO

Seismic System Performance HAM stack in air BSC stack in vacuum 102 100 10-2 10-4 10-6 10-8 10-10 Horizontal Vertical LIGO

Core Optics Substrates: SiO2 Polishing Coating 25 cm Diameter, 10 cm thick Homogeneity < 5 x 10-7 Internal mode Q’s > 2 x 106 Polishing Surface uniformity < 1 nm rms Radii of curvature matched < 3% Coating Scatter < 50 ppm Absorption < 2 ppm Uniformity <10-3 Production involved 6 companies, NIST, and LIGO LIGO

Core Optics Suspension and Control Optics suspended as simple pendulums Shadow sensors & voice-coil actuators provide damping and control forces Mirror is balanced on 30 micron diameter wire to 1/100th degree of arc LIGO

Feedback & Control for Mirrors and Light Damp suspended mirrors to vibration-isolated tables 14 mirrors  (pos, pit, yaw, side) = 56 loops Damp mirror angles to lab floor using optical levers 7 mirrors  (pit, yaw) = 14 loops Pre-stabilized laser (frequency, intensity, pre-mode-cleaner) = 3 loops Cavity length control (mode-cleaner, common-mode frequency, common-arm, differential arm, michelson, power-recycling) = 6 loops Wave-front sensing/control Beam-centering control 2 arms  (pit, yaw) = 4 loops LIGO

Suspended Mirror Approximates a Free Mass Above Resonance Blue: suspended mirror XF Cyan: free mass XF Data taken using shadow sensors & voice coil actuators LIGO

Frequency Stabilization of the Light Employs Three Stages Pre-stabilized laser delivers light to the long mode cleaner Start with high-quality, custom-built Nd:YAG laser Improve frequency, amplitude and spatial purity of beam Actuator inputs provide for further laser stabilization Wideband Tidal IO 4 km 15m 10-Watt Laser PSL Interferometer LIGO

Pre-stabilized Laser (PSL) Custom-built 10 W Nd:YAG Laser, joint development with Lightwave Electronics (now commercial product) Cavity for defining beam geometry, joint development with Stanford Frequency reference cavity (inside oven) LIGO

Interferometer Length Control System Multiple Input / Multiple Output Three tightly coupled cavities Ill-conditioned (off-diagonal) plant matrix Highly nonlinear response over most of phase space Transition to stable, linear regime takes plant through singularity Employs adaptive control system that evaluates plant evolution and reconfigures feedback paths and gains during lock acquisition LIGO

Digital Interferometer Sensing & Control System LIGO

Digital Controls screen example Digital calibration input Analog In Analog Out LIGO

Why is Locking Difficult? One meter Human hair, about 100 microns Earthtides, about 100 microns Wavelength of light, about 1 micron Microseismic motion, about 1 micron Atomic diameter, 10-10 meter Precision required to lock, about 10-10 meter Nuclear diameter, 10-15 meter LIGO sensitivity, 10-18 meter LIGO

Tidal Compensation Data Tidal evaluation on 21-hour locked section of S1 data Predicted tides Feedforward Feedback Residual signal on voice coils Residual signal on laser LIGO

Microseism: Effect of Ocean Waves Microseism at 0.12 Hz dominates ground velocity Trended data (courtesy of Gladstone High School) shows large variability of microseism, on several-day- and annual- cycles Reduction by feed-forward derived from seismometers LIGO

Commissioning Time Line LIGO

Noise Equivalent Strain Spectra for S1 LIGO

Background Forces in GW Band = Thermal Noise ~ kBT/mode xrms  10-11 m f < 1 Hz xrms  210-17 m f ~ 350 Hz xrms  510-16 m f  10 kHz Strategy: Compress energy into narrow resonance outside band of interest  require high mechanical Q, low friction LIGO

Thermal Noise Observed in 1st Violins on H2, L1 During S1 ~ 20 millifermi RMS for each free wire segment LIGO

Binary Neutron Stars: S1 Range LIGO Image: R. Powell

LIGO Sensitivity Over Time Livingston 4km Interferometer May 01 Jan 03 LIGO

Binary Neutron Stars: S2 Range LIGO Image: R. Powell

Binary Neutron Stars: Initial LIGO Target Range S2 Range LIGO Image: R. Powell

What’s next? Advanced LIGO… Major technological differences between LIGO and Advanced LIGO 40kg Quadruple pendulum Sapphire optics Silica suspension fibers Initial Interferometers Active vibration isolation systems Open up wider band Reshape Noise Advanced Interferometers High power laser (180W) LIGO Advanced interferometry Signal recycling

Binary Neutron Stars: AdLIGO Range Image: R. Powell

…and opening a new channel with a detector in space. Terrestrial Planning underway for space-based detector, LISA, to open up a lower frequency band ~ 2015 LIGO

Despite a few difficulties, science runs started in 2002. LIGO